RF rotary joints are electromechanical devices that consist of rotational (rotors) and stationary (stators) members. They allow the transmission of RF\ microwave signals and power from their rotors to stators or vise verse, and are used to change the direction of microwave propagation between two guides by rotating one with respect to other.
A conventional RF rotary joints consists of either a contacting or non-contacting interface to transfer RF\ microwave signals and power. In non-contacting rotating interfaces, electrical continuity for RF is typically achieved by using λ/4 chokes, to correspond to the quarter wavelength of a particular frequency which eliminate the need for physical contact at the rotating junction. The advantage of a non-contacting interface is that all physical wear is eliminated. Disadvantages of this approach are size and weight, particularly at lower frequencies, which have longer wavelengths and therefore require longer chokes.
In contacting rotating interfaces, two relative rotatable conductive parts keep sliding contact by spring, or other actuators. The advantage of a contacting rotating interfaces is that size can be greatly reduced when compared to a ¼ wavelength choke interface. Disadvantages of contacting rotating interfaces are increased torque, the need for a tight and perfectly concentric fit of the rotating interface, and the fact that contact stress in rotation causes wear and the wear debris would cause electrical failure at the rotating interface.
Examples of related art are described in U.S. Pat. No. 3,229,234 A, which pertains to a tinuity between a fixed and coaxial line operating in the dominant TEM mode and circular waveguide operating in the TMO1 mode that enables extremely broad band coverage. The method of maintaining continuity is not dependent upon the impedance of the transmission lines selected; and U.S. Pat. App. No. 2005\0264377A1, which pertains to a rotary cable connector assembly for connecting coaxial waveguides. The assembly includes a metal stator having a counter bored well and a metal rotor extending coaxially into the well. An axial air gap is formed between the stator and rotor which each contain a conventional dielectric sleeve and center element for mating conventionally to carry a signal there between. An electrical connector/dynamic RF shield for providing an electrical path across the rotary joint and for shielding the air gap includes a pair of rings having crenelated cylindrical leaves extending axially toward each other and being interspersed. Each ring has a face for making electrical contact with the stator and rotor. A spring urges the rings into contact with the stator and rotor. The crenelated leaves provide RF shielding of the air gap surrounded by the shield. The rings are formed of bronze or other non-precious metal or alloy.
Fiber brush technology has been successfully used in electrical slip ring industry, where, a brush assembly comprising a multifilament conductive fiber brush contacts with a conductive slip ring surface. The brush assembly is constructed with thousands of hair-fine silver alloy fibers running on their tips, offer significant improvement over carbon brushes in both data and current transfer, offering extended brush and slip ring service life, high current capacity, and significant decreases in service acoustic and electrical noise.
Examples of related art are described in U.S. Pat. No. 4,398,113 A, which pertains to a slip ring and brush assembly comprises a gold plated slip ring surface and a bundle of conductive fibers in the 2 to 3 mil size range. During use, gold transfers from the ring to the fibers, and the resulting gold-on-gold contact interface of ring and brush is extremely noise free and long wearing.
The Fiber optic Rotary Coupler is the optic equivalent of the electrical slip ring. It allows uninterrupted transmission of an optic signal in a fiber guide through a rotational interface to a stationary apparatus. The Fiber optic Rotary Coupler is widely used in missile guidance systems, robotic systems, remotely operated vehicles, oil drilling systems, sensing systems, and many other field applications where a twist-free fiber cable is essential. Combined with electrical slip rings or fluid rotary couplers, Fiber optic Rotary Coupler adds a new dimension to traditional slip rings. As fiber optic technology advances, more and more traditional slip ring users will benefit from Fiber optic Rotary Coupler in their new fiber systems.
Comparing with its electrical counterpart, the electrical slip ring, the Fiber optic Rotary Coupler is not easy to fabricate because the transmission of the light beam through a fiber is strongly depend on its geometrical structure and related position. So it requires special design to ensure the transmission of light beam through a relative rotating coupler without suffering a large loss.
Examples of related art of single channel fiber optic rotary coupler are described in:
U.S. Pat. No. 5,039,193, which pertains to a rotary joint for singlemode optical fibers, having a fixed and a rotating part to permit the transmission of optical signals across a rotational interface (such as a winch or turret) with minimal insertion loss and, in particular, low reflections (good return loss). There is no need of conversion to electrical signals; the device is passive. It may be use an oil of refractive index matched to that of the glass fibers and to that of fiber tapers or lenses used to expand the beam emitted from one fiber and contract it for transmission into the other fiber. The device is bidirectional. By use foil, through precision techniques for building and mounting the optical and mechanical components, and by use of advanced bearings, both the insertion loss and unwanted reflections (return loss) can be minimized, thereby making it suitable for use with singlemode fiber. Insertion loss can be further reduced in conjunction with index-matching fluid by using optical elements (lenses, tapers, fibers) having angled or curved facets rather than perpendicular facets. Oil filling has the further advantage of pressure compensation allowing the device to operate at any ambient pressure. Lenses having curved surfaces can be accommodated by the use of fluid having a refractive index different from that of the lens material.
U.S. Pat. No. 4,124,272, which pertains to a rotary fiber optic waveguide coupling. Bared ends of two fiber optic waveguide cable sections are held in mutually-aligned end-to-end adjacent positions in opposite extension along a common rotary axis by a pair of ferrules having central through-openings in which such ends coextend and are bonded in close fit. The ferrules are held in precise axial position by abutment at their inner ends with annular shoulder in a pair of alignment caps mounted in two members movable relatively about such rotary axis. Retaining sleeves screwed into the relatively turnable members cooperate with washer members on the ferrules to obtain such abutment, and the ferrules project through openings in the alignment caps to obtain precise radial positioning. A friction-free rotary bearing interconnects the two relatively turnable members. The bearing is preloaded along the axis of rotation to give precise axial and radial positions of the one turnable member relative to the other.
U.S. Pat. No. 5,633,963, which pertains to a rotary joint for optical fibers comprising a plug assembly and a first ferrule having a fiber-entry end mounted coaxially therein, a receptacle assembly and a second ferrule having a fiber-entry end mounted coaxially therein, wherein at least one of the plug-mounted ferrule and the receptacle-mounted ferrule is biased outwardly from a fiber entry-end of the ferrule, and an alignment sleeve for optically connecting the first and second ferrules and maintaining the optical connection during rotation of one of the plug assembly and the receptacle assembly about an axis parallel to a longitudinal direction of the assembly relative to the other of the plug assembly and the receptacle assembly.
U.S. Pat. No. 5,949,929, which pertains to a connection that includes an interventional medical device having a rotatable optical fiber, an assembly having a conduit for conveying a light beam to the rotatable fiber as well as a rotor and a fixed housing, and a coupling. A drive mechanism is attached to the rotor for continuously rotating the rotor. The coupling includes a rotatable portion attachable to a proximal end of the rotatable fiber and to the rotor so as to permit the rotatable fiber to rotate continuously with the rotor while the rotatable fiber remains in axial alignment with the light beam. The coupling also includes a stationary shield surrounding the rotatable portion. The stationary shield is attachable to the fixed housing so as to urge the rotatable portion and the rotor together. The proximal end of the rotatable portion of the coupling has a vee-shaped coupling surface that complements a distal end surface of the rotor. The rotor is at least partially hollow and includes a bearing that holds the light beam conduit in axial alignment with the rotatable fiber when the rotatable portion of the coupling engages the rotor. The rotatable fiber may be disengageable from the rotatable portion of the coupling when the stationary shield does not engage the fixed housing. The rotatable fiber may be surrounded by a sheath that is attachable to the stationary portion of the coupling. A fluid port connected to the stationary portion of the coupling enables introduction of fluid into the sheath and around the rotatable optical fiber.
U.S. Pat. No. 4,373,779, which pertains to a single channel optical slip ring assembly comprising a hollow rotor shaft selectively dimensioned for receiving a fiber optic cable, a rotor bushing mounted in the rotor shaft and having an axial bore for receiving an optic fiber of a fiber optic cable, a stator cylindrical member selectively dimensioned for receiving a fiber optic cable, and having on one end an axially extending collar, a stator bushing mounted within the stator proximate the collar having an axial bore for receiving an optic fiber in each end thereof, means for rotatably mounting the bushing end of the rotor shaft within the collar of the stator cylindrical member so that the rotor bushing bore and the stator bushing bore are aligned along the axis of rotation and the bushings are separated by a selected gap, a gauging bore in the stator bushing which orthogonally intersects its axial bore, means in the stator cylindrical member for permitting access to the gauging bore, a stator fiber optic cable in the stator cylindrical member having an exposed length of optic fiber extending into the stator bushing bore to a selected gauged location within the gauging bore, and a rotor fiber optic cable in the rotor shaft having an exposed length of optic fiber passing through the rotor bushing bore, across the gap, and into the stator bushing bore to a selected gauged location spaced from the stator optic fiber within the gauging bore, whereby the rotor optic fiber rotates within the stator bushing and the fiber ends are maintained spaced from one another and in axial alignment thereby.
Most of the aforementioned references employ the expanded beam technology, i.e., using lenses to expand the light beam and collimate it before transmitting to a rotary coupler. The beam is then refocused and aligned with the receiving fiber. The lenses include graded index rod lens, aspheric lens, and GRIN lens. This method has several significant drawbacks. First, this kind of rotary coupler require special fixture to have lenses aligned. Secondly, using high quality lenses would increase the sizes and cost of fiber optic rotary couplers. Further, to maintain the axial alignment is difficult so that this kind of rotary coupler is vulnerable in such environments as temperature change, vibration and shock.
Above all, none of the reference art described above addresses all of the issues that the present invention does. There exist ample unmet needs for a system having a plurality of conductive fiber brush bundles, a fiber optical wire and a coaxial conductor to transfer RF and optical signal(s) concurrently between relatively rotatable objects.